The SMTP service in MERCUR Messaging 2005 before Service Pack 4 allows remote attackers to cause a denial of service (infinite loop) via a message in which neither the originator nor recipient address is known.
https://exchange.xforce.ibmcloud.com/vulnerabilities/27230
http://www.vupen.com/english/advisories/2006/2354
http://www.securityfocus.com/bid/18462